<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <style>
    * {
        box-sizing: border-box;
        margin: 0;
        padding: 0;
    }

    div {
        height: 500px;
        width: 200px;
    }

    #main {
        width: 100%;
        float: left;
    }

    #content {
        margin: 0 200px;
        width: auto;
        background-color: red;
    }

    #left {
        float: left;
        margin-left: -100%;
        background-color: yellow;
    }

    #right {
        float: left;
        margin-left: -200px;
        background-color: blue;
    }
    </style>
</head>

<body>
    <div id="main">
        <div id="content">中间</div>
    </div>
    <div id="left">左边</div>
    <div id="right">右边</div>
</body>

</html>